1. Technical Field
Described herein is a semiconductor device including a MISFET.
2. Related Art
In a MISFET (Metal-Insulator-Semiconductor Field Effect Transistor), the problem of an increase in leakage current between the gate electrode and the substrate is caused by a direct tunneling phenomenon of carriers in a gate insulating film. To avoid such a tunneling phenomenon, formation of the gate insulating film with the use of a material having higher relative permittivity than SiO2 has been suggested. More specifically, the use of a high-dielectric metal oxide such as ZrO2, HfO2, a compound with SiO2, or silicate has been suggested.
Instead of conventional polycrystalline silicon, the use of a metal material for the gate electrode has been considered, to adjust degradation of characteristics due to depletion of the gate electrode and adjust the threshold voltage.
In a MISFET having a gate insulating film including a high-dielectric metal oxide layer, the TDDB (Time Dependent Dielectric Breakdown) lifetime of the gate insulating film is not sufficient to guarantee the device, and it is necessary to improve the reliability of the gate insulating film. To guarantee the lifetime of a device, the lifetime is determined in terms of the necessary area and percent defective by performing statistical processing. Particularly, in a MISFET having a gate insulating film including a high-dielectric metal oxide layer, the distribution of TDDB lifetime is reportedly too wide (as disclosed by S. Inumiya et al., in “DETERMINATION OF TIME TO BE BREAKDOWN OF 0.8-1.2 NM EOT HfSiON GATE DIELECTRICS WITH Poly-Si AND METAL GATE ELECTRODES”, IEEE 06CH37728, 44th Annual International Reliability Physics Symposium, Sa Joes, 2006, p.p. 184-188, for example). Therefore, in terms of the area and percent defective necessary for guaranteeing the device, the life becomes very short.